Blank characters preceding initial left parentheses or in-between of format specification

[gxyd]

Bug Description

Blank characters can precede the initial left parentheses of format specification. E.g. 2 (2I3, I5) is a valid format specification and so is 2 (2I 3, I5), and is to be interpreted the same way as 2(2I3, I5). Below is a screenshot from J3 SD-007r1.pdf (Draft Fortran 2023), pg 288, section 13.2:

Steps to reproduce

For the below Fortran program:

program main
    implicit none
    integer :: i, j
    i = 19
    j = 20
    print 9, i, i + 1, j + 1, i + 2, j + 2
    9 FORMAT (I12, /, ' Dates: ', 2 (2I3, I5))
end program main

on it's execution with LFortran, we get an output an output as below (without any error, but informing of unsupported format " "):

Printing support is not available for   format.
Printing support is not available for   format.
          19
 Dates:  20 21

while on execution of the above program with GFortran we get the below output:

          19
 Dates:  20 21   21 22

while if we try with space between the format specification itself:

program main
    implicit none
    integer :: i, j
    i = 19
    j = 20
    print 9, i, i + 1, j + 1, i + 2, j + 2
    9 FORMAT (I12, /, ' Dates: ', 2 (2I 3, I5)) ! notice the space `2I 3`
end program main

LFortran raises a tokenizer error:

tokenizer error: Token '2' is not recognized in `format` statement
 --> test.f90:1:2
  |
1 | program main
  |  ^ 

which seems to be the correct output.

System information

macbook air m1

[gxyd]

I'll look into the issue.